Radio scanning is a typical operation included in two-way radios to allow users to rapidly scan multiple channels. Many applications of radio scan require that once a radio detects qualified channel activity, the user should be able to listen and answer back on that channel.
Typically, two-way radios provide the option of using tone-coded-squelch (TCS) signaling during transmissions and receptions. This subaudible signaling reduces false squelch bursts and squelch tails. If a scanning radio detects radio frequency (RF) channel activity that uses TCS signaling, in order for the user to be able to answer back, the radio must determine the TCS frequency being used on the RF channel.
Methods that can accurately determine the presence of a single particular TCS frequency (i.e., predictive TCS frequency determination) on a channel do exist. Scanning with these predictive TCS frequency determination methods can be relatively efficient if the radio is scanning particular RF channels looking for a single TCS frequency. However, if the TCS frequency is unknown and the radio is essentially scanning all possible standard TCS frequencies on particular RF channels, accurately determining the TCS frequency can be time consuming.
As seen in prior art FIG. 1, scanning starts 101 where the receiver is set up on a specific channel 103. If no radio RF carrier 105 is detected, the next channel is selected 107 and the receiver is set up on the next channel 103. The channels are scanned iteratively 103, 105, 107 from a list until a carrier is detected. Upon completion of scanning the list, scanning continues again from the beginning of the list. If an RF carrier is detected 105, the receiver starts checking for the first 109 of n 111 standard TCS frequencies using a predictive TCS detector 113. If the TCS frequency is detected 115, note the standard TCS frequency number as the decoded TCS frequency 119. If the TCS frequency is not detected 115, then increment to the next standard TCS frequency 117. Upon completion of checking all the standard TCS frequencies 111, the next channel to scan is selected 107. If a standard TCS frequency is detected 115, then the standard TCS frequency detected is noted as the decoded TCS frequency 119 and receiver is unmuted 121. The decoded TCS frequency can be displayed and used by the radio to answer back. The receiver is unmuted 121 until channel activity ceases 123. When channel activity ceases 123, the next channel to scan is selected 107.
It is highly desirable that a radio providing a scanning feature to scan channels as fast as possible. However, the technique described in FIG. 1 may significantly increase scan time since each standard TCS frequency is sequentially checked when RF channel activity is detected. Thus, the need exists to provide a method of efficiently scanning channels in which the determination of an unknown TCS frequency on a channel is required.